Synonym: challenge, dispute, mistrust, question, suspect. Similar words: no doubt, without doubt, double, double up, double back, subtle, trouble, troubled. Meaning: [daʊt] 
n. 1. the state of being unsure of something 2. uncertainty about the truth or factuality of existence of something. v. 1. consider unlikely or have doubts about 2. lack confidence in or have doubts about.
n. 1. the state of being unsure of something 2. uncertainty about the truth or factuality of existence of something. v. 1. consider unlikely or have doubts about 2. lack confidence in or have doubts about. 
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(241) There is no doubt that the court's decision is a victory for common sense.
(242) There is no doubt it was an accident and I bear no grudges.
(243) Lest anyone should doubt my story, I have brought documents to attest to its truth.
(244) He'd been behaving so strangely that they began to doubt/question his sanity.
(245) There seems no reason to doubt the sincerity of his beliefs.
(246) He is in no doubt as to what is needed.
(247) She is without doubt the best student I have ever taught.
(248) There's no doubt that one day a cure will be found.
(249) There is no doubt now that her marriage is beyond repair.
(250) Everyone knows what's best for him or herself. He/she or he can also be used in writing:If in doubt, ask your doctor. He/she can give you more information. These uses can seem awkward when they are used a lot. It is better to try to change the sentence, using a plural noun. Instead of saying:A baby cries when he or she is tired you can say Babies cry when they are tired.
(251) The arrangements for the event still seemed to be in doubt.
(252) My son and his girlfriend have had yet another row, but no doubt they'll patch it up by the weekend.
(253) She was beyond all doubt the finest ballerina of her day.
(254) Whenever she was in doubt,she often flipped up a coin.
(255) This latest evidence casts serious doubt on his version of events.
(256) She was a top student,(sentencedict.com) no doubt about it .
(257) I doubt whether her motives for donating the money are altruistic - she's probably looking for publicity.
(258) I have no doubt at all in my own mind about this.
(259) Without doubt this was the most important relationship I developed at college.
(260) I have not the slightest shadow of doubt about that.
(261) She is without a doubt the best tennis player I know.
(262) Something Lucy said began to sow seeds of doubt in his mind.
(263) The contract for this will no doubt be widely advertised.
(264) Natalie is, without a doubt, the star student in this year's ballet class.
(265) She may have been lying(Sentence dictionary), but I felt I had to give her the benefit of the doubt.
(266) He gave his word that he would marry her and she had no cause to doubt him.
(267) New witnesses have cast doubt on some of the evidence that sent the 19 year old to the gallows.
(268) We have no reason to doubt the essentials of the girl's story.
(269) I'll try to come, thoughI doubt if I'll be there on time.
(270) I doubt whether/if I can finish the work on time.
More similar words: no doubt, without doubt, double, double up, double back, subtle, trouble, troubled, dour, do up, dough, hand out, hold out, in and out, weed out, stand out, send out, find out, washed out, spread out, tremendous.